This invention relates generally to the field of focussing electromagnetic radiation, and more particularly to a multiple image photolithography system and method.
Integrated circuits are produced from wafers of silicon or some other semiconductor material. A typical process for producing an integrated circuit includes photolithography. The design of the circuit to be produced requires that certain surface portions of the silicon have specific electronic characteristics. Those characteristics are modified by exposing the silicon to other elements that migrate into the silicon crystal. Because the change in conductivity is desired only in certain areas, a material is used to coat the silicon and impede the migration. Photolithography is used to remove the coating from only those surface areas where migration, and the concomitant modification of electronic characteristics, is desired. Photolithography is also used to place conductive materials at specific points on the wafer. The manufacture of liquid crystal devices and magnetic heads may also include the use of photolithography.
The smaller the scale at which electronic characteristics can be manipulated, the more circuit elements can fit onto a chip of given area. More features may also be included in a liquid crystal device or magnetic head of a given size as a result of more exacting photolithography. As the size of circuit elements has decreased, photolithography equipment has become more exacting so that greater resolution can be achieved. Replacing a photolithographic stepper in order to increase the resolution and the depth of focus is very expensive. Large capital costs delay the improvement of photolithographic resolution.
Photolithography may be employed many times in the manufacture of a single device. For example, an integrated circuit may be formed of over twenty layers, the pattern for each layer projected onto the device using photolithography. Over the course of adding many layers to a device, the surface of the device may develop undulations. In may be desired that the photolithographic equipment be able to focus the pattern of light on a surface with varying vertical dimensions. New generations of photolithographic steppers are able to focus radiation with greater precision across the surface of the wafer or other device, i.e., in the horizontal dimensions. As the precision of focus in the horizontal direction is increased, the range in the vertical direction over which this precision occurs in decreased. The range over which the image stays in focus in the vertical dimension is called the depth of field. Thus, it may be desired to focus radiation very narrowly in the surface dimensions and maintain that focus over some range in the vertical dimension.
Accordingly, a need has arisen in the art for an improved photolithography system. The present invention provides a multiple image photolithography system and method that substantially reduce or eliminate problems associated with prior photolithography systems.
In accordance with the present invention, a multiple image photolithography system includes a radiation source. The radiation source provides electromagnetic radiation that is then projected along a path. The system also includes a radiation-sensitive material located in the path of the projected radiation. A reticle cartridge is located in the path of the projected radiation between the radiation source and the radiation-sensitive material. The reticle cartridge contains a photomask and a Fabry-Perot interferometer. The photomask and interferometer are located in the photomask so as to lie in the path of the projected radiation.
More specifically, in accordance with one embodiment of the present invention, the reticle cartridge is positioned with the photomask preceding the interferometer in the projected radiation path.
Also in accordance with the present invention, a method for projecting multiple radiation images onto photoresist includes inserting a substrate with a photoresist coating into a stepper and positioning the photoresist within the path of radiation projected by a radiation source in the stepper. A Fabry-Perot interferometer and a photomask are inserted into the stepper and each is positioned in the radiation path with the photomask between the interferometer and the radiation source. Radiation is projected from the radiation source, passes through the photomask and interferometer and then reaches the photoresist.
Technical advantages of the present invention include improving the depth of focus of the radiation pattern projected by a stepper onto a radiation-sensitive material. Another technical advantage is allowing for a Fabry-Perot interferometer to be placed within and removed from the radiation path of a stepper without expensive modifications to the stepper. Another technical advantage is an increase in the pattern resolution without the large capital cost of upgrading stepper equipment. Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Individual embodiments of the invention do not necessarily include all the technical advantages.